Intact electroplaques will be isolated from the electric organ of the eel, Electrophorus electricus, so that the permselective mechanism of both the electrically and chemically excitable regions of the innervated face may be explored. The kinetics of voltage dependent changes in both the potassium conductance system and the spike- generating sodium conductance system of the electrically excitable areas of this membrane will be examined. Qualitative and quantitative comparisons can then be made to related excitable system. The chemically excitable regions yield an excitatory post-synaptic potential in response to nerve stimulation. The ionic nature and the kinetics of the associated conductance changes will be explored. Both voltage and current-clamping techniques will be used. Threshold and other phenomena which may help to clarify the processes controlling ionic diffusion across both types of membrane will be investigated. The electrical effects produced at one major surface of the cell in response to alterations of the medium bathing the opposite surface will be investigated to gain insight into intracellular regulatory mechanisms.